In the graphic printing and plate-making art, the demand for reduced processing time is increasing recently for achieving the commercial benefits of short delivery and effective working. A fixing time of up to 19 seconds is desired in order to provide an overall processing time of 60 seconds or less. In processing photosensitive materials of large size used in the graphic plate-making art such as scanner film, contact lith film, and facsimile film, however, a fixing time of up to 19 seconds will lead to short fixation, particularly at the center of the photosensitive material. Also a correspondingly reduced washing time can lead to short washing, adversely affecting image retention.
One possible approach is to reduce the amount of silver halide in photosensitive material, but is generally accompanied by a lowering of maximum density. In the graphic printing photosensitive material application where reducing treatment may be carried out, a silver amount of at least 2.0 g/m.sup.2 is preferred, that is, the silver amount cannot be reduced below a certain limit.
Conventional approaches for improving fixing speed include an increase of fixing temperature and increased agitation in the fixing tank which both often suffer from local fixing marks. In extreme cases, for example, increased fixing temperatures will cause liquid evaporation, giving off smell, and evaporated sulfide gas will attack the surrounding equipment in the room.
Another approach is to increase the amount of fixer circulated through the fixing tank. Enhanced circulation provides increased fixing ability in proximity to the solution inlet and outlet of the tank, but is less effective near the center. Effective fixation near the tank center is achieved only by considerably increasing the amount of fixer circulated, but excessive fixation then takes place in proximity to the inlet and outlet, resulting in a waste of energy.
From the standpoint of fixer composition, a common approach for increasing the fixing speed is to increase the concentration of a fixing agent, typically thiosulfate. This approach, however, was impractical because of the following limitations. (a) Fixation is rather retarded when the thiosulfate concentration exceeds 2 mol/liter. (b) Since the washing time is short due to rapid processing, a higher fixing agent concentration would lower washing efficiency, resulting in a larger amount of residual hypo and poor image retention. (c) The fixer and wash water add to the environmental pollution load. (d) Concentration of the fixer is difficult and requires an increased cost.
It was also proposed to substitute organic compounds for the thiosulfates as the fixing agent. One fixing agent to substitute for the thiosulfates is a meso-ionic compound, 1,2,4-triazolium-3-thiolate as disclosed in U.S. Pat. No. 4,378,424 and Japanese Patent Application Unexamined Publication (JP-A) No. 150842/1982 wherein only an embodiment using a fixing agent consisting solely of a meso-ionic compound is described.
JP-A 201659/1989 discloses to add meso-ionic thiolate compounds to bleaching or bleach-fixing bath as a bleaching promoter; and JP-A 44355/1990 discloses the use of a bleaching solution containing ferric diethylenetriamine pentaacetate and a fixer containing a 1,2,4-triazolium-3-thiolate in the processing of color photosensitive material. However, none of these references teach the use of meso-ionic compounds in a fixer for the rapid processing of black-and-white silver halide photosensitive material (without using a bleaching solution) as proposed in the present invention and the benefits associated therewith.
Additionally, meso-ionic compounds are disclosed in U.S. Pat. Nos. 4,003,910, 4,624,913, 4,631,253, and 4,675,276, and JP-A 144737/1985, 176920/1986, 96943/1987, 217237/1987, 253161/1987, 287239/1987, 3641/1989, and 154056/1989 wherein the meso-ionic compounds are added to either photographic photosensitive materials or developers. None of these references teach the use of meso-ionic compounds in a fixer as proposed in the present invention and the benefits associated therewith.